VB.NET WinForms中如何刷新DbContext数据？

Hey Pascal, let's walk through how to nail both of these requirements—fetching fresh database data when selecting a new row in your DataGridView, and refining your entity update workflow. Here's a step-by-step breakdown tailored to your scenario:

The key here is to avoid relying on the cached entity bound to the grid, and instead pull the latest state directly from the database using a new DbContext. Here's how to implement it:

1. Hook up the SelectionChanged event for your DataGridView. You can do this either in the designer or in your form's constructor:

   public YourForm()
   {
       InitializeComponent();
       dataGridView1.SelectionChanged += DataGridView1_SelectionChanged;
   }
   

2. Implement the event handler to fetch fresh data:

   private void DataGridView1_SelectionChanged(object sender, EventArgs e)
   {
       // Exit if no row is selected
       if (dataGridView1.SelectedRows.Count == 0) return;
   
       // Get the bound entity from the selected row (replace YourEntity with your actual entity type)
       var selectedCachedEntity = dataGridView1.SelectedRows[0].DataBoundItem as YourEntity;
       if (selectedCachedEntity == null) return;
   
       // Use a new DbContext to avoid cached data
       using (var freshContext = new YourDbContext())
       {
           // Fetch the latest version using the entity's primary key
           var freshEntity = freshContext.YourEntities.Find(selectedCachedEntity.Id);
           
           if (freshEntity != null)
           {
               // Populate your detail UI controls with the fresh data
               txtEntityName.Text = freshEntity.Name;
               txtEntityDescription.Text = freshEntity.Description;
               // ... map other properties to your form controls
           }
       }
   }
   

   Why a new DbContext? Because the original context used to populate the grid might have cached the entity—using a fresh one ensures you get the most recent data from the database, including changes made by other users or processes.

You're already on the right track with creating a new DbContext and using the selected row's bound item. Let's polish this to ensure updates work reliably:

private void btnSaveChanges_Click(object sender, EventArgs e)
{
    if (dataGridView1.SelectedRows.Count == 0) return;

    var selectedCachedEntity = dataGridView1.SelectedRows[0].DataBoundItem as YourEntity;
    if (selectedCachedEntity == null) return;

    using (var updateContext = new YourDbContext())
    {
        // Fetch the entity from the database first (critical for EF to track changes)
        var entityToUpdate = updateContext.YourEntities.Find(selectedCachedEntity.Id);
        
        if (entityToUpdate != null)
        {
            // Apply changes from your form controls to the fetched entity
            entityToUpdate.Name = txtEntityName.Text;
            entityToUpdate.Description = txtEntityDescription.Text;
            entityToUpdate.LastUpdated = DateTime.Now;
            // ... update all relevant properties

            // Save changes to the database
            updateContext.SaveChanges();

            // Refresh the DataGridView to show the updated state
            RefreshDataGridView();
        }
    }
}

// Helper method to reload the DataGridView with fresh data
private void RefreshDataGridView()
{
    using (var context = new YourDbContext())
    {
        dataGridView1.DataSource = context.YourEntities.ToList();
        // Optional: Re-select the updated row after refresh
        var updatedRow = dataGridView1.Rows.Cast<DataGridViewRow>()
            .FirstOrDefault(r => (r.DataBoundItem as YourEntity)?.Id == selectedEntityId);
        if (updatedRow != null) updatedRow.Selected = true;
    }
}

Key Notes for the Update Workflow: #

• Always fetch the entity from the update DbContext first—EF needs to track the entity to detect changes and save them correctly. Don't modify the cached entity from the grid directly.
• After saving, refresh the DataGridView to ensure all users see the latest data.
• If your entity doesn't have a simple primary key (to use Find), use FirstOrDefault with a unique identifier instead:

  var entityToUpdate = updateContext.YourEntities
      .FirstOrDefault(x => x.UniqueIdentifier == selectedCachedEntity.UniqueIdentifier);
  

内容的提问来源于stack exchange，提问作者Pascal